Magnesium titanate phosphor



Patented Aug. 16, l949 2,479,158 msnnsnnrxrrrms'm rnosrnone Herman CIFFoelicli, Cleveland fieights flhio ass siinoriftdsfiineralElectricsCompany ascorporatinnof New York lmzmwingsefippifiationJanuarF-J'E'HB EYQ Serial No. 7225.45?

My invention relates generally to phosphors, that is, fluorescent orphosphorescent materials. More particularly, my invention relates tomagnesium titanate phosphor, and it is an object of this invention toprovide an improved composition of high brightness, as well as animproved method of compounding and preparing the phosphor. Moreparticularly, it is an object to provide a simple method whereby thephosphor may be prepared by a single firing at comparatively lowtemperature so that the cost of preparing the phosphor is verysubstantially less than that involving firing at the usual hightemperature. Further objects and advantages of my invention will appearfrom the following detailed description.

According to the present invention the phosphor is prepared by firing,at 1070 C., a dry mixture of MgO. TiOz, a manganese compound capable ofbreaking down to furnish MnO, such as MnCOa or MnFz, and some -20% byweight of the total of AlF3. The mixture is obtained by short ballmilling or repeated sieving through a fine mesh screen. Within limits,the phosphor is not very sensitive to change in matrix composition. Therange of 2-4 mols MgO for one mol TiOz gave the brightest phosphor.Powders having a ratio of less than 1:1, however, were substantiallyless bright, while powders with a much, higher ratio than 4:1 were alsoinferior because of dilution by inert MgO. The range of optimumconcentration of the MnO activator is narrow; it

was found to lie between about .01 and .1% by A considerable variety ofadded impurities, in-

,cluding ZrOz, SnOz, SbzOa, ZnO, showed little effect. Even relativelylarge amounts of iron. and copper did not impair the brightness unduly.Phosphates, however, proved to be harmful.

The dry method described herein is superior to the wet method which isnot only expensive but very troublesome when larger amounts areprepared. The hydrolysis of TiCh even in concentrated I-ICl is stronglyexothermic and is accompanied by evolution of large amounts of HCl gas.

To make the phosphor more friable, some beryllium oxide may beincorporated in it. Thus a phosphor made with 2 mols MgO and one mol BeOfor one mol TiOz was of the same brightness, but more friable, ascompared with a phosphor having 3 mols of MgO for one mol TiOz.

The following is one specific example for the 1 preparation of thisphosphor. 30 grams mag- 4 Claims. (Cl. 252301.4)

nesium oxide and 30 grams TiOz (both commercial grades of preferablyhigh purity), 9 grams 'fine particle size, are sifted 5 times throughmesh bolting cloth. The powder mixture is then placed on a silica trayand. fired in an electric furnace in air at 1070 C. for one hour. Aftercooling, crushing and sieving, the phosphor may, if desired, be refiredin oxygen at 560 C. for 15 hours. After cooling it is again sifted andis then ready for use.

Analysis of diffraction patterns has shown that high phosphor brightnessis associated with the development of the spinel-type orthotitanatecompound, 2MgC x TiOz. Brightness is low when the structure ofmetatitanate MgO x TiOz prevails. Metatitanate is produced in mixturescontaining only one mol MgO for one mol TiOz. It is also produced whenmixtures containing more than one mol MgO react incompletely to givemetatitanate plus excess free MgO.

The function'of aluminum fluoride is apparently twofold. It acts as aflux, catalyzing the formation of the fluorescent spinel-typeorthotitanate, especially in mixtures having at least 2 mols MgO foreach mol of TiO2. In addition, however, it also enters the spinellattice as part of a new complex compound in which Ti and O are partlyreplaced by Al and F ions. Evidence {for this complex titanate is acontraction of the spine] lattice containing incorporated AlFs, ascompared with orthotitanate prepared without any AlFs;

The further addition of BeO does not produce any additional latticechanges, indicating that BeO is probably not incorporated within theorthotitanate lattice. It serves, apparently, merely as a diluent,though as a useful one, because it increases the friability of thephosphor.

The phosphor is particularly responsive to longer ultraviolet radiationsof, for example, 3650 A. wave length. It fluoresces with a red color,and may be used in conjunction with high pressure mercury vapor electricdischarge lamps to supplement the spectrum of such lamps by the additionof red light.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of preparing a magnesium titanate phosphor which comprisesfiring at a temperature of approximately 1000 to 1200 C. a; dry mixtureof MgO and TiOz in proportions of about 2 to 4 mols MgO for 1 mol-TiOz.a manganese compound capable of breaking down to aluminum fluorideactivated by manganese in an amount of from .01 to 0.1%by'we'ight of V i15 Number MnO, the aluminum fluoride being present in an amount of about10 to 20% by weight.

4. A fluorescent material consisting of a com-- plex compound ofmagnesium orthotitanate and aluminum fluoride activated by manganese inan amount of from .01 to 0.1% by weight of mo, the aluminum fluoridebeing present in an amount of about 10 to 20% by weight, and themagnesia and titania being present in proportions of about 2 to 4molsMgO to 1 mol Ti02.

' HERMAN C. FROELICH.

REFERENCES CITED The following references are of record in the file ofthis patent: I

"UNITED STATES PATENTS Name Date Krautz June 3, 1941

